The present invention relates to a traction modifying differential, and more particularly, to such a differential of the type in which the differential gearing may be locked in response to an electrical input signal.
Traction modifying differentials of the type to which the present invention relates typically include a gear case defining a gear chamber, and disposed therein, a differential gear set including at least one input pinion gear, and a pair of output side gears. A clutch pack is typically disposed between at least one of the side gears and an adjacent surface of the gear case, such that the clutch pack is operable to limit relative rotation between the gear case and the one side gear. In most differentials of the type described, engaging the clutch pack is achieved by one of several different approaches.
In one approach, a xe2x80x9clocking differentialxe2x80x9d of the type illustrated and described in U.S. Pat. No. Re 28,004, assigned to the assignee of the present invention and incorporated herein by reference, the clutch pack is normally disengaged. When one of the wheels begins to spin out, relative to the other wheel, a speed sensitive mechanism senses the speed differential and, by means of a ramping mechanism, locks the clutch pack solid. Thereafter, both outputs of the differential rotate at the same speed.
U.S. Pat. No. 5,019,021, also assigned to the assignee of the present invention and incorporated herein by reference, illustrates another approach, a xe2x80x9climited slip differentialxe2x80x9d in which the loading on the clutch pack may be varied in response to an external electrical input signal, thus varying the amount of slip within the clutch pack, and therefore, the amount of bias torque transmitted from one side gear to another. As is well known to those skilled in the art, in a limited slip differential, there is typically a certain amount of xe2x80x9cslipxe2x80x9d, or speed differential, between the two side gears whenever the vehicle encounters less than optimum traction conditions.
Although the performance of limited slip and locking differentials of the type shown in the above-incorporated patents is, in general, quite satisfactory, there are certain disadvantages of each particular design, for certain vehicle applications. The requirement for at least one, and typically two clutch packs, adds substantially to the overall cost of the differential, especially when at least some of the individual clutch disks are provided with a relatively more sophisticated friction material, able to withstand elevated temperatures under continuous slipping conditions.
In addition, there are many vehicle applications in which it would be desirable to provide a traction modifying differential, to replace an existing open differential, but wherein the traction modifying differential would have to fit within the same space currently occupied by the open differential, in order to avoid a complete redesign of the surrounding structure. In such a situation, the addition of one or two clutch packs, within an existing differential case, would be impossible without redesigning the pinion gears and side gears and downsizing them, which is typically not feasible.
In an attempt to overcome the disadvantages of the differential devices noted above, the assignee of the present invention has developed an improved locking differential which is illustrated and described in an earlier application which was co-pending with the parent application of the present application, the earlier application having now issued as U.S. Pat. No. 6,083,134 for an xe2x80x9cElectronically Actuated Locking Differentialxe2x80x9d, assigned to the assignee of the present invention, and incorporated herein by reference. In the device of the cited patent, an electromagnetic coil initiates ramping of a ball ramp actuator in which one ramp plate is disposed outside of the differential case, while the other ramp plate is disposed within the differential case. There is a set of balls engaging the two ramp plates, the balls being disposed in slightly oversized openings in the end wall of the differential case. The ramp plate disposed within the differential case defines a set of teeth which are disposed to engage a mating set of teeth defined by the adjacent side gear, whenever the ball ramp actuator is displaced from its normal, centered condition to a ramped condition.
Although the differential device of the cited patent provides an improved locking differential which may be actuated in response to an external electrical signal, and may be either engaged or disengaged very quickly, and which is quite compact, there are however certain vehicle applications for which the device does not have sufficient strength, referring primarily to the differential case, and more particularly to the end wall having the cut-outs for the balls of the ball ramp actuator.
One of the problems commonly associated with locking differentials has been the inability of the differential to xe2x80x9cdisengagexe2x80x9d from the locked condition when such is no longer needed. Typically, locking differentials have been able to unlock only in response to an event such as a torque reversal.
Accordingly, it is an object of the present invention to provide a further improved locking differential of the general type illustrated and described in the cited patent, but which has improved overall strength and torque transmitting capability.
It is a more specific object of the present invention to provide such an improved locking differential which accomplishes the above-stated object by substantially reducing the size of any cut-out portions in the differential case end wall which are necessitated by the presence of the ball ramp actuator.
It is a related object of the present invention to provide such an improved locking differential which is capable of locking in response to an electrical input signal.
The above and other objects of the invention are accomplished by the provision of a differential gear mechanism including a gear case defining an axis of rotation and a gear chamber. Differential gearing is disposed in the gear chamber and includes at least one input gear and first and second output gears. The mechanism includes means operable to limit rotation of the first output gear relative to the gear case for common rotation therewith. The mechanism further includes actuation means for the rotation limiting means, the actuation means including first and second actuating plates comprising a cam and ramp type actuator, wherein relative rotation of the first and second actuating plates from an unactuated condition to an actuated condition is effective to move the rotation limiting means toward an engaged condition. The second actuating plate is disposed, in the unactuated condition, to rotate with the gear case, an electromagnetic actuator is disposed adjacent the second actuating plate and is operable, in response to an electrical input signal, to cause rotation of the second actuating plate relative to the gear case.
The improved differential gear means is characterized by the first and second actuating plates being disposed external to a gear case end wall, and the first actuating plate being axially moveable toward the end wall and having associated therewith a plurality of actuation members extending axially through the corresponding openings in the end wall. The rotation limiting means comprises a locking portion fixed for rotation with the first output gear. The locking portion and the plurality of actuation members cooperate to provide means for locking the first output gear in a non-rotatable locked position relative to the gear case, when the first actuating plate moves toward the end wall, moving the actuation members toward a locked position relative to the first output gear.